Types of Errors

1. Client Errors (4xx)
   These happen when the user or client makes a mistake.
   Examples:

   • Invalid input data
   • Missing parameters
   • Unauthorized access

✔ Responsibility: Client-side

 

2. Server Errors (5xx)
   These occur when the server fails to process a valid request.
   Examples:

   • Database failure
   • Internal bug
   • Server overload

✔ Responsibility: Server-side

Why Understanding Errors Matters

If you don’t understand errors:

• Debugging becomes difficult
• Users get confused
• Systems become unreliable

If you handle them well:

• Developers can fix issues faster
• Users get clear guidance
• Your API feels professional and trustworthy

Technical Example

Here, the server is not “failing” it is correctly informing the client about what went wrong.

Real-Life Examples

1. Online Shopping (Client Error – 400 Bad Request)

You try to place an order but forget to enter your address.

• System response: “Address field is required”
• What happened? → You gave incomplete input

API Meaning:
Client sent wrong/insufficient data → 400 Bad Request

2. Login Attempt (Client Error – 401 Unauthorized)

You enter the wrong password while logging in.

• System response: “Invalid username or password”
• What happened? → Authentication failed

API Meaning:
User is not verified → 401 Unauthorized

3. Server Crash While Booking (Server Error – 500 Internal Server Error)

You try booking a movie ticket, but the server crashes.

• System response: “Something went wrong. Please try again later.”
• What happened? → Problem on server side

API Meaning:
Server failed internally → 500 Internal Server Error